Slide-valve oe steam-engines



DAVID STODDART, OF SAN FRANCISCO, CALIFORNIA.

SLIDE-VALVE or STEAM-ENGINES.

Specification of Letters Patent No, 25,146, dated August 16, 185,9;

To all whom it may concern:

Be itV known that I, DAVID STODDART, of the city of San Francisco, in the county of San Francisco and State of California, have invented certain new and useful Improvements i-n Means of Relieving the Slide- Valves of Steam-Engines of Unnecessary Pressure; and I do hereby declare that the following is a full, clear, and exact description of the same, reference being had to the accompanying drawing, forming part of this specification, in which- Figure l, is a longitudinal, central section of a steam chest, valve and valve seat, in a plane perpendicular to the face of the valve, showing the application of my invention. Fig. 2, is a transverse section of the same, in the plane indicated by the letters an, Fig. l. Fig. 3, is a face view of the valve. Fig. 4, is a back view of what I term the balance frame.

Similar letters of reference indicate corresponding parts in the several figures.

To enable others to apply my invention, I will proceed to describe it with reference to the drawings.`

A, is the steam chest; a, a, the valve seat, which is raised above the bottom of the steam chest, and B, the slide valve. C, is the balance frame, faced to tit the back of the valve which is parallel with the face thereof, and D, the flexible plate securing the balance frame to the cover E, of the steam chest.

The exible plate D, is made of sheet copper or brass, and secured at its edges to the steam chest cover by clamping the said edges between the said cover and the upper marginal portion of the steam chest, to which it is bolted. A cavity b, b, is made in the interior of the cover, and the pressure of steam in the chest keeps the said plate in contact with the cover except where this cavity b, b, exists. The balance frame is made of brass or other suitable metal, of a width equal to the whole width of the valve seat and its length is equal to the distance between the inner margins of the steam ports s, s, in the valve seat except that it has four horns c, c, c, c, viz, one at each side of each end, of a width equal to the width of the parts of the valve seat at the ends of the ports, and of a length from end to end of the horns equal to the entire length of the valve seat. The horns are to give the balance frame the required area without making it cover the steam ports s, s, so that the steamv pressure will always be on the valve perpendicularly over the ports. The said frame has a square upward projection d, d, which is secured by bolts f, j', to the liexible plate D, to make a steam tight joint therewith and it has a central opening c', corresponding in size, form and position with an opening in the center of the said plate.

The valve is substantially like the slide valves commonly used, except that it is made with two horns g, g, at its ends, of a length as per drawing, and of a width equal to those on the balance frame, so that no portion of the bottom of the balance frame may be exposed to the pressure of steam, and that it has a narrow opening h, in its back to communicate with the opening i, inthe balance frame and lexible plate and to bring the space at the back of the plate into communication with the exhaust port e, and thus prevent any accumulation of steam behind the said plate. The portions j, y', of the valve seat outside of the steam ports are made of no greater width than is necessary to make a tight valve.

The full area of the balance frame in the example of my invention represented, is equal to the whole area of the valve seat; i. e. the raised face on which the valve works minus the combined areas of the two steam ports s, s, and the portions j, y', at the ends of the seat, so that the greatest pressure toward its seat that can possibly be produced by the direct action of the steam upon the valve is equal to the combined areas of the ports and the lap at the two ends of the valve, but this pressure can only take place on the admission of steam after the valve has been stopped at the center of its stroke which is never likely to occur in practice, and when in its operation the valve arrives in such a position (except in cases where there is a very great lap) steam is always in one of the ports s, s. The greatest pressure toward its seat ever produced by the direct pressure of steam on the valve at work, is when it is at its extreme throw, when the pressure is equal to the combined areas of one steam port and one of the strips j, j, of the seat. This direct pressure of the steam upon the valve is all that it endures, for the downward pressure on the balance frame is perfectly balanced by the upward pressureof the steam upon the portion of the flexible plate surrounding the proj eetions eZ, CZ, within the edge of the cavity Z), Z1. Only a portion of this pressure acts on Y the balance fra-me, the remainder acting projections (Z, cl, should be so proportioned that the proportion of the said pressure, which, by the law which governs the resolution of forces, is caused to be transmitted to the balance frame, will be just s uiieient to balance the downward pressure on the eX- posed part of the said frame. If, however, it should be desirable to allow a little down ward pressure of steam on the balance frame to keep it in contact with the valve and compensate for wear of the said frame and the valve and seat, it may be done by properly proportioning` the flexible plate, but I prefer to give the pressure necessary to compensate for such wear, by means of a spring m, applied within the cavity b, b, of the steam chest cover to press upon the said frame and to adjust the pressure of the said spring by means of a set screw n, screwing through the steam chest cover.

What I claim as my invention and desire to secure by Letters Patent, is

l. The employment of the elastic plate D, in combination with a cavity (b) and a balance frame C, substantially as and for the purpose herein shown and described.

2. The combination of an adjusting spring (m) and screw n with the elastic plate D,

substantially as and for the purpose herein U shown and described.

DAVID STODDART. lVitnesses ROBERT STODDART, ELIZA J. STODDART. 

